Researchers mapping hot spots to reduce costs

Farmers looking for ways to control damaging levels of tarnished plant bugs as economically as possible may soon have help from two research projects being conducted in Louisiana and Mississippi.

The projects are aimed at using landscape management techniques and remote sensing technology to help growers reduce the severity of infestations and the cost of insecticide applications for tarnished plant bugs in cotton.

“Tarnished plant bugs are becoming more of a post-bloom than an early-season problem in Louisiana,” says Ralph Bagwell, Extension entomologist with the LSU AgCenter in Winnsboro, La. “In some areas, growers are now having to make six to nine insecticide applications for plant bugs per season.”

That sharp increase in applications — and the cost associated with them — is due to two factors:

“We're no longer getting the collateral control we used to have because of pyrethroid resistance in the tobacco budworm, boll weevil eradication and Bt cotton,” he said. “And we're seeing an increased abundance of alternate wild hosts due to more CRP/WRP acreage and reduced farm profitability.”

Bagwell noted that Louisiana has experienced a dramatic increase in land enrolled in the Conservation Reserve and Wetlands Reserve programs in the last five years. Since 1997, Louisiana farmers have more than doubled their CRP and WRP acreage (to 350,000 acres).

“Land in the CRP or WRP can harbor a lot of weeds that serve as alternate hosts for tarnished plant bugs,” says Bagwell. “Gordon Snodgrass (of the USDA/ARS Southern Insect Management Research Unit at Stoneville, Miss.) has counted 169 wild hosts for tarnished plant bugs in the Delta region.

“Depending on how growers manage them, these CRP or WRP acres can become a reservoir for insects moving into our row crops.”

A group of researchers at the LSU AgCenter and USDA/ARS and Mississippi State are conducting a study aimed at managing landscapes or pre-cotton hosts to manage in-season populations of tarnished plant bugs.

The researchers include R.W. Costello and Gene Burris at LSU's Northeast Research Station in St. Joseph, La.; and Roger Leonard at the Macon Ridge Branch Station in Winnsboro, La.; Snodgrass, William Scott and Dick Hardee at USDA/ARS in Stoneville; and J.T. Robbins with Mississippi State University in Starkville, Miss.

While tarnished plant bugs may overwinter on nearly 170 different plants, researchers are focusing on a small group of broadleaf weeds that seem to be more prevalent in the Delta landscape. Among those are henbit, shepherdspurse, curly dock, fleabane, Carolina geranium, common chickweed, cutleaf eveningprimrose and white clover.

Research indicates that tarnished plant bug adults and nymphs build in those hosts in field borders in the spring and begin moving into crops when the winter or early spring weeds senesce or die back.

When the researchers burn down the weeds in the field borders with a herbicide, they see some reduction in the number of tarnished plant bug adults and nymphs in neighboring cotton fields. (Herbicides used include such products as the glyphosate compounds, Roundup, Touchdown and others; Gramoxone Max; and Valor.)

“In April and May, the researchers are observing significantly higher numbers of tarnished plant bugs in the non-treated areas,” says Bagwell. “The reductions in populations in cotton fields have not been statistically significant, possibly due to boll weevil eradication and applications by the producer.

“But we believe that once growers started managing the landscape over a large area, it could have an impact on in-field tarnished plant bug numbers.”

In the second project, researchers are testing the viability of using remote sensing technology to variably apply insecticides to control tarnished plant bugs in cotton fields.

The study, conducted jointly by researchers with LSU and USDA-ARS and private industry, has shown cost savings of up to 35 percent for variable applications compared to whole-field applications of pesticides.

“The objective we've been working on is to reduce insect control costs by applying insecticides only to areas where insect densities are highest,” said Bagwell. “Stated another way, we want to reduce costs by applying insecticides where the potential for economic return is highest.”

Researchers and crop consultants have observed that insect populations tend to be clumped, generally in areas of more-vigorous plant growth. Researchers believe they can use this tendency to precision-apply insecticides.

“Insects go to areas with the bigger, more-vigorous plants,” says Bagwell. “So we should be able to treat these hot spots with insecticides and curtail the applications on the rest of the field. If the insects aren't in those locations, they're probably not in the field.”

Producers like Jay Hardwick of Newellton, La., and Kenneth Hood of Gunnison, Miss., have been making variable rate applications of plant growth regulators for several years. It wasn't too much of a leap to adapt the technology to insecticides.

Bagwell and Leonard with LSU, Jeff Willars with USDA/ARS at Stoneville, Michael Seal with ITD Spectral Visions, the National Cotton Council, and Hardwick and Hood have been working together to “ground test” the assumptions to see if they can accomplish real cost savings.

The research team uses NDVI (Normalized Difference Vegetative Index) images taken from a satellite or by airplane to determine the more-productive areas of the fields. Those are correlated with the crop consultant's knowledge of the field history to produce a prescription application map.

The map is downloaded so the variable applicator's on-board computer can turn the sprayer on and off as it goes across the field.

“The economic analysis of the study by Kenneth Paxton at LSU is showing savings of about 35 percent in insect control costs,” says Bagwell. “We're also not seeing any decrease in yields. In fact, we're observing a slight increase.”